The present invention is directed to certain alkylated alkanolamines as a hydraulic cement admixture and to cement compositions containing same. Specifically, alkylated alkanolamines described herein have been found capable of lowering the air content and related porosity of cement compositions.
The term cement is used to designate many different kinds of materials useful as binders or adhesives. Hydraulic cements are powdered inorganic materials which, when mixed with water, form a "paste" that hardens slowly. If further mixed with fine aggregate (e.g. sand), it forms a "mortar" and if mixed with both fine and coarse aggregate (e.g. sand and stone) it forms a "concrete" which are rock-hard products useful in structural formations. These products are commonly referred to as hydraulic cement compositions or mixes. These compositions are commonly formed from portland cements (conforms to ASTM C-150), blended cements (containing large amounts of slag or pozzolanic materials, etc.) and the like.
Various additives have been used in hydraulic cement compositions to alter mixing and curing properties and conditions as well as to alter the properties of the resultant cured product of the hydraulic cement composition.
When concrete is formed, it requires mixing of the various components (hydraulic cement, sand, gravel, water and possibly cement additives) to a substantially uniform mixture. In the course of the mixing, air becomes entrapped in the composition and much of this air remains in the resultant cured hydraulic cement composition in the form of voids. If the amount of voids is large, the mix is said to be "air entrained". In most instances, a small amount of air entrainment is tolerated and, in certain instances, it is desired (to enhance the freeze/thaw properties of the concrete). However, in warmer climates, air entrainment in the hydraulic cement composition is not a desirable feature as it causes the resultant structure to have lower compressive strength than the mixture design is capable of attaining. There is an inverse relationship between air entrainment and compressive strength. It is generally believed that for each 1 volume percent of air bubbles contained in a concrete mass, the concrete mass loses about 5 percent of its compressive strength.
It is known that certain cement admixtures used for their beneficial effects also have a detrimental side effect of causing excessive air entrainment. Such cement additives include certain water-reducing agents and superplasticizers such as lignin sulfonates, naphthalene sulfonate polymers and the like; strength enhancers and set accelerators such as triisopropanolamine triethanolamine, respectively, and the like. The reduction of entrained air, whether due to mixing technique, admixture effect or the like, is highly desired to provide a structure which closely approaches its design strength and which has low permeability and, therefore, is not susceptible to attack by corrosive elements and the like which could permeate into the structure during its useful life.
Various materials are presently used in the cement industry to reduce the amount of air contained in cured hydraulic cement compositions. Conventional air-detraining agents are generally viewed as surfactants having low hydrophilic-lipophilic balance (HLB) values, such as tri-n-butylphosphate, n-octanol and the like. Normally, these agents have been found difficult and somewhat ineffective to use in commercial applications for several reasons. Firstly, they can not be readily introduced into dry concrete mixes due to the difficulty in dispersing the additive throughout the cement to provide a uniform distribution of the small amount of agent required. Further, the conventional air detrainers are not miscible with and, therefore, not capable of being added with other conventional cement admixtures as such admixtures are invariably water-based compositions. When it is attempted to incorporate an air-detrainer into an aqueous admixture composition, it tends to separate out and is not properly supplied to the cement composition to be treated. Recently, "water-dispersible" air-detrainers have been introduced in an attempt to overcome this problem. These agents still have low HLB values and are actually not water soluble but merely have densities close to that of water. Nevertheless, these agents phase-segregate and are unstable in aqueous suspension in storage and, thus, have the same defects of prior known air-detrainers.
Air-detraining agents are generally very powerful in their effectiveness and, therefore, must be used in very small amounts which must be substantially uniformly distributed throughout the cement composition being treated. Presently known air-detraining agents have the disadvantages of being difficult to monitor and control in terms of dosage and distribution in cement compositions, thus causing the composition to exhibit unwanted variation from the desired degree of aeration (due to over or under dosage) and/or variation in aeration within the formed structure (due to poor distribution of agent).
It is highly desired to provide a water-soluble, readily dispersible material which is capable of providing air-detraining to cement compositions, in particular concretes.